Nordstrom and Inman (1975) conducted a study of wave climate and beach 

 response at Torrey Pines Beach, north of La Jolla; beach profiles were 

 measured at approximate monthly intervals during June 1972 to April 1974. 

 Pawka, et al. (1976) reported the wave climate recorded by offshore pres- 

 sure sensors up to four times daily from February 1973 to May 19 74. Dur- 

 ing the study, Torrey Pines Beach underwent seasonal changes in config- 

 uration related to changes in wave regime. High-energy winter waves re- 

 moved sand from the subaerial beach and deposited it offshore at depths 

 less than 30 feet below mean sea level (MSL) . Low-energy summer waves 

 returned sand to the subaerial beach from depths less than 20 feet be- 

 low MSL. 



Figure 5 shows the offshore survey data along the three ranges dur- 

 ing the Torrey Pines Beach study (App. B in Nordstrom and Inman, 1975). 

 Measured sand level changes were less than 2 feet beyond a water depth 

 of about 21 feet relative to MSL, and less than 1 foot beyond a water 

 depth of about 26 feet relative to MSL. These fathometer profile surveys 

 have a stated accuracy of ± 1 foot, so recorded changes less than 1 foot 

 indicate profile closure. The reference rod arrays at 24 feet below MSL 

 showed ranges in sand level of 1.2 to 1.5 feet during the study; arrays 

 at 33 feet below MSL showed ranges of 0.2 to 0.4 foot, with a stated 

 measurement accuracy of 0.3 foot. These data show that 26 feet below 

 MSL is the limit depth to the active profile at the study site. 



A characteristic yearly design wave should be chosen considering 

 both the breaker observations tabulated in Appendix D of Nordstrom and 

 Inman (1975) , and the offshore wave measurements tabulated in Appendix 

 D of Pawka, et al. (1976). Among the 470 daily observations during 23 

 months, 10- foot-high breakers were noted three times, with a 14-second 

 period on 12 February 1973, an 18-second period on 28 February 1973, and 

 a 10-second period on 18 April 1973. Among the 657 wave measurements dur- 

 ing 16 months, the most energetic condition was reported as 3,840 square 

 centimeters, centered at a period of 14.2 seconds on 12 February 1973; 

 this energy level corresponds to a significant deepwater height of 7.2 

 feet, and a significant height of 8.0 feet in a 33- foot depth. The den- 

 sity of either wave data set is not sufficient to make the extreme tab- 

 ulated condition represent a 12-hour per year duration, so a higher wave 

 should be chosen as the design condition. A nearshore height of 10 to 

 11 feet and a period of 10 to 18 seconds seem appropriate design wave 

 conditions for this locality. For these conditions, equation (6) gives 

 depths of 20.3 to 23.9 feet. At Torrey Pines Beach, mean lower low water 

 is -2.7 feet relative to MSL; adding this possible tidal effect to the 

 calculated depth results in a limit depth estimate of 23.0 to 26.6 feet 

 relative to MSL. Thiis , the proposed calculation procedure gives an ac- 

 curate estimate of the actual limit depth to the active profile in this 

 case. 



V. CONCLUSION 



Using the number introduced in equation (2) and several quantitative 

 assumptions, the water depth at a hypothetical seaward limit of intense 



17 



